Microbio 310 1st Edition Lecture 28 Outline of Last Lecture I. 29.7 AntibodiesII. 29.8 Antibody ProductionIII. 29.9 Antibodies, Complement, and Pathogen DestructionIV. 30.1 Innate Immunity and Pattern RecognitionV. 30.2 Adaptive Immunity and the Immunoglobulin SuperfamilyVI. 30.3 MHC Protein StructureVII. 30.4 MHC Polymorphism and Antigen BindingVIII. 30.5 Antibody Proteins and Antigen BindingOutline of Current Lecture I. 30.6 Antibody Genes and DiversityII. 30.7 T Cell Receptors: Proteins, Genes, and DiversityIII. 30.8 Clonal Selection and ToleranceIV. 30.9 T Cell and B Cell ActivationV. 30.10 Cytokines and ChemokinesVI. 31.1 Isolation of Pathogens from Clinical SpecimensVII. 31.2 Growth-Dependent Identification MethodsVIII. 31.3 Antimicrobial Drug Susceptibility TestingIX. 31.4 Safety in the Microbiology LaboratoryThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.X. 31.5 Immunoassays for Infectious DiseaseXI. 31.6 Polyclonal and Monoclonal AntibodiesXII. 31.7 In Vitro Antigen–Antibody Reactions: SerologyXIII. 31.8 AgglutinationXIV. 31.9 ImmunofluorescenceCurrent Lecture30.6 Antibody Genes and Diversity• The immune system must be able to generate an almost unlimited antibody variation– Done using a limited number of genes• Ability to produce almost limitless antibody diversity is due to:– Somatic recombination– Random heavy and light chain reassortment – Coding for joint diversity– Hypermutation (polymerase makes mistakes in hopes it changes and amino acid and allows the antibody to bind to a different antigen)• The gene encoding each immunoglobulin is constructed from several immunoglobulin gene segments (“genes in pieces” hypothesis)– Allelic exclusion• At least 1.92 million possible antibodies can be expressed!• Antibody diversity is expanded in B cells by somatic hypermutation (higher mutation rates)30.7 T Cell Receptors: Proteins, Genes, and Diversity• TCRs bind both self MHC and foreign peptides• TCRs and MHCs bind directly to peptide antigen• The CDR3 regions of both the alpha and beta chains bind to the epitope, whereas the CDR1 and CDR2 regions bind to the MHC protein• TCR diversity is generated by a variety of genetic mechanisms– lpha and eta chains are encoded by distinct gene segments for constant and variable domains • Somatic recombination• Random chain reassortment • Coding for joint diversity (mistakes made at joining regions that contribute to diversity)30.8 Clonal Selection and Tolerance• T cells must be able to distinguish between self and nonself antigens• Unresponsiveness to self is called tolerance (must be tolerant of self)– To acquire tolerance, lymphocytes are maintained that interact only with the nonself antigens derived from dangerous pathogens– Failure to develop tolerance may result in dangerous reactions to self antigens called autoimmunity•  Clonal selection theory– Each antigen-reactive B or T cell has a cell surface receptor for a single antigen epitope • When stimulated, the cell replicates• Positive selection – T cells that recognize MHC peptides are retained• Negative selection– T cells that pass the positive selection and strongly bind to self antigens are selected against• Clonal deletions– More than 99% of T cells that enter the thymus do not survive the selection process because either they do not interact with MHC or they interact too strongly with MHC– Remaining T cells react strongly with foreign antigens30.9 T Cell and B Cell Activation• T and B cells require two molecular signals for activation– First signal is interaction with antigen through immunoglobulins or TCRs– A second signal is necessary for them to respond to antigens• T cells not yet exposed to antigen are called naive or uncommitted T cells– Must be activated by an APC to become competent effector cells• B cell activation is initiated by interaction between antigen and surface immunoglobulin• The second signal involves several molecules– Interaction between B cell CD40 protein and CD40L on the T cell causes release of cytokines– Cytokine IL-4 stimulates antibody production30.10 Cytokines and Chemokines• Intracellular communication in the immune system is accomplished by a heterogeneous familyof proteins called cytokines (signaling molecules)– Over 50 cytokines are known– Regulate cellular functions and activate various cell types– Cytokines produced by lymphocytes are called lymphokines or interleukins (ILs)– Interferons (IFNs) and tumor necrosis factors (TNFs) act on cells other than B and T lymphocytes• Chemokines (signaling molecules)– Are a small group of proteins that function as chemoattractants for phagocytes and lymphocytes– Produced by lymphocytes and other cells in response to bacterial products, viruses, or other pathogenic agents that cause cell damage– About 40 chemokines are known31.1 Isolation of Pathogens from Clinical Specimens• Specimens must be obtained and handled properly– Specimen should be obtained from site of infection– Sample must be taken aseptically– Sample size must be large enough– Metabolic requirements for the organism must be maintained during sampling, storage, and transport (specimen needs to be able to be cultured)• Most microbes of clinical importance can be grown, isolated, and identified with specialized growth media– General-purpose media• Support growth of most aerobic and facultatively aerobic organisms (e.g., bloodagar) – Enriched media• Contain specific growth factors that enhance growth of certain fastidious pathogens (need very precise chemically defined media)– Selective media• Allow some organisms to grow while inhibiting others (ex: high levels of salt in media so only organisms that can survive in high salt environments grow)– Differential media• Allow identification of organisms based on their growth and appearance on themedium• Blood Cultures– Bacteremia• The presence of bacteria in the blood • Uncommon in healthy individuals– Septicemia• Blood infection– Blood cultures are the only immediate way of isolating and identifying the causative agent of septicemia• Urine Cultures– Urinary tract infections are common, especially in women (older people can die of UTI)– Disease-causing agents are often normal flora– Dipstick tests can be used to